The present invention relates to processing of various signals (e.g., audio, video, and images) with embedded auxiliary data, or “watermarks”, that are provided, e.g., for copyright protection purposes.
The promises of online distribution of digitized content are accompanied by an increasing threat of piracy. Digital content, such as digital music, video and still images, can now be freely communicated over computer networks such as the Internet. The entertainment industry is contemplating the opportunities of electronic commerce, where the true value of the product (the digital content) is dissociated from any particular physical medium (such as a compact disc (CD), digital video disc (DVD), or the like). While it enables a greater degree of flexibility in its distribution and a lower cost, the commerce of disembodied information raises serious copyright issues. Indeed, digital data can be re-packaged, duplicated and re-distributed at virtually no cost, potentially turning piracy into a simple “click and drag” process.
The usage and distribution of digitized content can reasonably be controlled as long as it remains within a proprietary format (or “secure environments”). However, the wide availability of various open formats makes it easy for any user to capture the content and re-package it outside this “secure environment”. This is typically the first stage of a pirate distribution scheme.
For example, a user may purchase an audio CD anonymously from a store. The user may then extract (“rip”) the audio content of this CD with a general purpose personal computer (PC). The user may further compress the resulting audio files using some arbitrary open source compression utility (MP3 for instance). Finally, the user may wish to redistribute (free of charge or not) the resulting shorter, compressed files through a free or low-cost online distribution scheme such as email, File Transfer Protocol (FTP) or Hypertext Transfer Protocol (HTTP). This kind of piracy is a great threat to the music industry, and it can be generalized to other types of contents and industries. For example, audio renditions of books, as well as lectures, interviews, educational and business presentations, and the like, are all subject to piracy. Audio/video data, such as movies, is similarly subject to piracy.
It naturally follows that various usage and copy control applications call for solutions that allow viewer/player/copying devices or systems to detect whether an acquired copy of valuable content (e.g., the audio content to be protected) has undergone any such illicit re-packaging.
A way to achieve this goal is to design a system that quantifies the amount of processing that was applied to the valuable content since it was originally distributed. For this purpose, the use of a volatile data layer is a commonly accepted concept. This volatile data layer, sometimes referred to as a “Fragile Watermark,” is embedded within, or packaged along with the valuable content it protects. As the content is transferred onto a different medium type (or a different format), this volatile data layer is typically expected to be lost. Such a vanishing mark is also typically used in collaboration with a persistent data layer (e.g. a “Robust Watermark”), which is intended to survive such re-packaging of the valuable content, while signaling that the original copy of the content carried a volatile data layer. When the viewer/player/copying device or system is presented with the resulting copy of the content, it will look for this volatile data if the persistent data layer indicates that it should be there. The presence of such persistent data and the absence of the volatile data layer is an indication that the content was re-packaged. Clearly, such volatile data should be resistant to forgery. Indeed, the ability of a non-authorized entity (e.g., pirate) to create (or re-create) such volatile data is the major threat scenario in the context of such systems.
Regardless of the actual methodology that is suggested by the prior art to carry the volatile and the persistent data layers, these proposals all share similar concept for the desired behavior of a Fragile Watermark layer. Moreover, these proposals suggest a binary state for such a volatile data layer. That is, the fragile watermark layer is considered to be either present or absent. Moreover, the volatile data is designed to be removed by very small manipulations of the content. In other words, with prior art schemes, the volatile, fragile watermark data can only survive a perfect bit-for-bit digital copy of the content.
While such prior methodologies might be adequate to authenticate an original copy of digitized content, their usefulness is challenged by the emerging concept of legitimate versus illegitimate manipulations. Indeed, conflicts between consumer rights and the content providers' (e.g., entertainment industry's) interests are drawing a rather fuzzy line between what consumers can and cannot do with an original copy of valuable content they purchased. If a system based on volatile data is used to prevent multi-generational copying (i.e., making a first copy of an original, making a second copy from the first copy, and so forth), it should also be able to preserve the consumer's rights regardless of the technological limitation of their equipment. As an example, a consumer should be allowed to make a first generation copy of audio content he/she purchased (such as on a portable medium such as a CD, or downloaded via a network such as the Internet to a computer storage device), even if his/her audio (CD) capturing equipment does not provide perfect digital transfers. For example some digital captures may involve digital-to-analog-to-digital conversions. Also, some CDs may have minor scratches that are patched over by a digital interpolation with only a minor degradation in quality, but still not making a perfect signal copy. Further, a high resolution audio signal (e.g., 96 kHz sampling rate, 24 bit per sample resolution) can be copied into the lower resolution CD format of 44.1 kHz sampling rate, 16 bit per sample resolution. Here again, the signal copy is not perfect. All such copies may be allowed, while content manipulations involving perceptual compression methods (such as MPEG) may be prohibited.
In contrast to the prior art, the present invention introduces a softer concept for a Fragile Watermark. While the proposed watermarking layer of the present invention is designed to be prone to degradation, it is also designed to degrade gracefully, as opposed to disappearing after any arbitrarily minor manipulation of the content. The present invention further suggests an appropriate analysis that uses this graceful degradation in the context of a content-dependent fragility analysis, to derive a quantitative measurement of the amount of “processing” that was applied to the valuable content. The “processing” includes manipulations such as analog-to-digital conversions, resampling, reduction in bit depths (number of bits per sample), band-limiting, perceptual compression, collapsing multi-channel audio into stereo or mono (for audio content), recording on analog media, and digital or analog broadcast.
Another objective of the present invention is to provide consumers with a quality assurance tool. Generally, it can be hard for the consumer to establish if the digital object he has acquired (digital music, image, video, etc.) is of high quality, matching that of the master copy, or if it has been degraded through distribution channels. Using the herein proposed Fragile Watermark, and appropriate detection hardware and/or software, it is possible to quantify the damage suffered in the distribution channel without directly comparing the content to the master copy.
Moreover, the fragility analysis component of the present invention can be used for a variety of other applications. Indeed, the analysis of the content's intrinsic fragility can be measured to inform a user that a watermark he/she is about to embed within the content is not going to survive in a selected channel. In cases where the content is explicitly produced with a known mode of distribution in mind, the user may wish to compensate for such content-dependant fragility and increase the strength of the watermark he/she is about to embed appropriately.
The present invention provides a data processing system having the above and other advantages.